Hydrogen-based fuel cells for automotive and stationary applications are gaining popularity for various reasons, including their higher efficiencies and lower emissions. However, using pure hydrogen as a fuel in automotive and residential applications has many limitations. The infrastructure to deliver hydrogen is presently inadequate, the refueling of gaseous hydrogen can be slow, and the safe storage of hydrogen is problematic. Hence, using an onboard reformer to produce a hydrogen rich stream from fuels like gasoline and methanol is gaining popularity. The alternatives of producing hydrogen range from futuristic solar energy-based hydrogen generation to more pragmatic hydrocarbon reforming. Use of liquid and/or gaseous hydrocarbon fuels to generate hydrogen is being proposed as an immediate solution for environmentally friendly energy production. Besides favorable economics and the relative ease of reforming, this option is more practical since the existing distribution network can be utilized.
The conversion of hydrocarbon fuels to hydrogen can be carried out by several processes, including hydrocarbon steam reforming (HSR), partial oxidation (POX), and auto-thermal reforming (ATR). Hydrocarbon steam reforming involves the reaction of steam with the fuel in the presence of a catalyst to produce hydrogen and CO as given in equations (1) and (2) for methane, CH4, and isooctane, C8H18 (2,2,4-trimethylpentane which is used as a surrogate for gasoline). Since steam reforming is endothermic, some of the fuel must be burned in an external furnace and the heat transferred to the reformer via heat exchangers.

Partial oxidation involves the reaction of oxygen with fuel to produce hydrogen and CO as illustrated in equations (3) and (4), when the oxygen-to-fuel ratio is less than that required for total combustion, i.e., complete conversion to CO2 and H2O.

Partial oxidation can be conducted with a catalyst (catalytic partial oxidation) or without a catalyst (non-catalytic partial oxidation). The reaction rates are much higher for partial oxidation than for steam reforming, but the hydrogen yield per carbon in the fuel is lower. Non-catalytic partial oxidation requires reaction temperatures above 1000° C. to achieve rapid reaction rates. Although the reaction is exothermic, some of the fuel must be combusted because the amount of heat generated by the reaction is not sufficient to preheat the feed to achieve optimal rates. Recently, there has been interest in catalytic partial oxidation since it operates at lower temperatures than the non-catalytic route. The lower operating temperatures provide better control over the reaction, thus minimizing coke formation and allowing for a wider choice of materials of construction for the reactor.
Auto-thermal reforming involves the reaction of oxygen, steam, and fuel to produce hydrogen and CO2, and can be viewed as a combination of partial oxidation and steam reforming as given in equations (5) and (6). In essence, this process can be viewed as a combination of POX and HSR.

The choice of the reaction process to be used for on-board reforming depends on many factors, including the operating characteristics of the application (e.g., varying power demand, rapid start-up, and frequent shutdowns) and the type of fuel cell stack. HSR is heat transfer limited and as such does not respond rapidly to changes in the power demand (i.e. “load following”). When power demand rapidly decreases, the catalyst can overheat, causing sintering, which in turn results in a loss of activity. ATR can overcome the load following limitations of HSR, because the heat required for the endothermic reaction is generated within the catalyst bed, a property that allows for more rapid response to changing power demands and faster startup.